A Nevada man who once tried—unsuccessfully—to prove that he owned the world’s biggest emerald is putting a gem that he actually owns on the block: a 21,000-carat emerald that’s locked in a Florida vault.

Anthony Thomas, who filed for bankruptcy in March after losing his battle for the 840-pound Bahia Emerald, has already found a buyer for his 50-pound emerald.

But Mr. Thomas’s financial problems are a side story in the scarcely believable history of the Bahia Emerald, which has torn friends apart, sat underwater after Hurricane Katrina and kept teams of lawyers busy in court fighting over who owns it.

Not Mr. Thomas, a state judge recently determined.

In court papers, Mr. Thomas said his smaller emerald is worth more than $200 million but refused to say how much the potential buyer has offered. His lawyers, who did not return several messages, blacked out the purchase price in the five-page sale agreement filed to the U.S. Bankruptcy Court in Reno.

“Disclosure of the actual purchase price for the emerald poses a risk to my family and I,” Mr. Thomas said in court papers.

The proposed buyer, Koyo Shipping And Trading Corp., could not be reached either.

Mr. Thomas said the sale money will be enough to pay off their more than $6.3 million in debt, including a 2007 loan for smartcard-technology company that he managed and that no longer exists. Mr. Thomas said that he and his wife are unemployed.

Mr. Thomas is one of many people who have claimed ownership of the Bahia Emerald since it was discovered in Brazil in 2001. The gem, which is rumored to have protruding shards of forest green gem as round as “a man’s thigh,” once appraised for $925 million.

Mr. Thomas was in Sao Paulo shortly after the discovery to look for emeralds that could be used as collateral to borrow money for businesses. He said he bought the Bahia Emerald for $60,000, but the gem never arrived in the mail.

Mr. Thomas shrugged it off as local corruption and later heard that it had been jackhammered into pieces.

In reality, the gem’s journey—as told by National Geographic—included a stint at an abandoned gas station in California and another spell somewhere in New Orleans where it sat submerged after the 2005 hurricane. It was also involved in a $197 million banking deal with Bernard Madoff. However, Mr. Madoff was arrested just two days before the transaction was to be completed.

Mr. Thomas reentered the picture in 2008 when he heard the Los Angeles County Sheriff’s department had the emerald. In the lawsuit he filed to claim it, Mr. Thomas argued that the sale papers that proved he bought it for $60,000 had burned down in a 2006 house fire.

At least two judges haven’t believed Mr. Thomas’s tale.

Mr. Thomas and his wife, Wendi, filed for bankruptcy on March 4, near the end of the ownership dispute. Several weeks before the filing, a Los Angeles judge ruled that Mr. Thomas didn’t own the Bahia Emerald, but Mr. Thomas’s lawyer said he needed time to look for any legal options that remained. When a person files for bankruptcy, his or her legal disputes is usually stayed.

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From Dow Jones Daily Bankruptcy Review, exclusive coverage of corporate bankruptcies, companies headed for trouble and the latest trends in bankruptcy law, distressed investing and corporate restructuring. Lead writer Pat Fitzgerald and Daily Bankruptcy Review reporters in Washington, New York and Wilmington, Del., provide insight into the big cases, who’s next to fall and what’s making news across the bankruptcy market.